Review: Artificial liver support systems

A Simple Method for Hepatocyte Attachment in Hollow Fibre Bioreactors

A new method for hepatocyte attachment in hollow fibre (HF) bioreactors was proposed and verified. A flow of medium with suspended hepatocytes, evoked by transmembrane pressure (TMP), and directed across the membrane into the fibre lumen, has accelerated and improved hepatocyte contact with the HF. It was found that seeding of hepatocytes onto the membrane was optimal at TMP of 50–80 mmHg. Ammonia utilisation and ureagenesis rates in hepatocytes seeded in the bioreactor suggests that the proposed method warrants proper conditions for cell functionality and allows for extended culture of hepatocytes in HF bioreactors. It is speculated that time cutback between introduction of hepatocytes into the bioreactor and the start of the cell attachment process, accomplished by the presented method, leads to substantially improved recovery of freshly isolated hepatocytes, and consequently to better overall performance of HF bioreactor.

Mass Transfers in a Fluidized Bed Bioreactor using Alginate Beads for a Future Bioartificial Liver

Fluidized bed bioreactor with alginate beads may be an alternative to hollow fiber cartridge to host hepatocytes for bioartificial liver purposes. After the bioreactor design and the characterization of fluid mechanics, the present study was aimed at analyzing bi-directional mass transfers of calibrated species between external fluid and empty beads. Static (batch) and dynamic (fluidized bed bioreactor) experimental conditions were analyzed. A simple modelling approach permitted the definition of mass transfer coefficients.

The motion of beads within the bioreactor clearly enhanced mass transfer kinetics, but did not alter the amount exchanged. The shear enhanced diffusion coefficient for VitB12 was 20 times higher in the fluidized bed bioreactor than under batch conditions, proving the efficiency of such a device.

Alginate-Encapsulated Human Hepatoma C3A Cells for use in a Bioartificial Liver Device - The Hybrid-Mds

Purpose

The aim of this study was to encapsulate C3A cells into alginate microcapsules with an average diameter of ≤ 100 μm, thus enabling them to be recirculated in a bioartificial liver device based on MDS (Microsphere-based Detoxification System) technology. The microcapsules have to be permeable for essential proteins such as albumin.

Methods

C3A cells were encapsulated using alginate. The resulting alginate beads were coated with poly(diallyldimethylammoniumchloride) (pDADMAC) and poly(sodium-p-styrenesulfonate) (pSS). Their mechanical stability was tested by recirculation of the microcapsule suspension, while their permeability was determined by reverse-size exclusion chromatography and by the use of a confocal laser microscope. The metabolic activities of encapsulated C3A cells were compared to freely growing adherent C3A cells in static cultivation models. The metabolic functionality of encapsulated C3A cells in static conditions was compared to encapsulated C3A cells in a dynamic model.

Results

The mean diameter of the resulting microcapsules was 86 μm. Our experiments show that these microcapsules were permeable for albumin and the high flow rate of 600 ml/min in a dynamic model has no influence on the survival and the metabolic activities of the encapsulated cells during the tested time of 24 hours.

Conclusions

Alginate microcapsules containing C3A cells can be used to produce albumin and growth factors in a bioartificial or hybrid liver support system. Thanks to their small diameter, the microcapsules in suspension can be recirculated in the MDS.

Formation of porcine hepatocyte spherical multicellular aggregates (spheroids) and analysis of drug metabolic functions

Porcine hepatocytes are used in the hybrid artificial liver support system that we are developing because of their high level of liver functions in vitro and because human hepatocytes can not be used in Japan for ethical reasons. Spherical multicellular aggregates or spheroids have been found to be effective in vitro for long-term maintenance of liver functions. Therefore, we formed spherical multicellular aggregates (spheroids) of primary porcine hepatocytes using a polyurethane foam (PUF) as a culture substratum and analyzed their drug metabolic functions in vitro. Primary porcine hepatocytes inoculated into the pores of a flat PUF plate (25 x 25 x 1 mm), spontaneously formed spheroids within the range of 100 to 150 mum in diameter 24 to 36 h after inoculation. The formed spheroids were attached to the bottom surface of the PUF pores, and their morphology and viability were maintained for more than 12 days. The P-450 activity in the spheroids of porcine hepatocytes was demonstrated by detecting production of monoethylglycinexylidide from lidocaine. In addition, the conjugation enzyme activity was demonstrated by detecting glucuronidation and sulfation of acetaminophen. These activities were maintained for 12 days at a level twice as high as in the monolayer culture. This result shows that the porcine hepatocyte spheroids formed by using PUF can maintain the drug metabolic functions important in a hybrid artificial liver device. Consequently, culturing porcine hepatocyte spheroids using PUF seems to be promising for development of a hybrid artificial liver.

Analysis of the ammonia metabolism of rat primary hepatocytes and a human hepatocyte cell line Huh 7

Ammonia metabolism of ratprimary hepatocytes and a human hepatocyte cell line,Huh 7, at different concentrations of glutamine,glucose and ammonia was examined. During theincubation of the primary hepatocyte cells, glutamineand ammonia concentrations decreased, that of ureaincreased, and that of glucose remained the same. Inthe case of Huh 7 cells, glucose was consumed rapidly,the concentration of ammonia increased and that of urearemained the same. The major energy sources amongmedium components were glutamine for the primary cellsand glucose for Huh 7 cells, although the primaryhepatocytes may utilize intracellular glycogen asenergy source. As the glutamine concentration in theincubation medium increased, the specific rates of notonly glutamine consumption, but also ammonia productionby the primary cells and Huh 7 cells increased. Besides, specific urea production rate by the primarycells increased then. Increase of glucoseconcentration had no effect on glutamine and ammoniametabolism by both cells, although it increased glucoseconsumption by Huh 7 cells. The incubation of theprimary cells with higher ammonia concentrationincreased all specific rates of glutamine consumption,ammonia consumption and urea production. An increasein the ammonia concentration to 5 mM changed theammonia metabolism from production to consumption andincreased the specific glucose consumption rate. Consequently, increases in the glutamine and ammoniaconcentrations were revealed to have negative andpositive effects, respectively, on decreasing ammoniaconcentration by both of rat primary hepatocytes andHuh 7 cells.

Cryopreservation of primary porcine liver cells in an organotypical sandwich model in a clinically relevant flat membrane bioreactor

To overcome the logistical difficulties of continuously supplying freshly-isolated, primary porcine liver cells to bioartificial liver support bioreactors, we developed a cryopreservation method using an organotypical sandwich model in a flat membrane bioreactor (FMB). We measured albumin secretion rate, urea synthesis rate and 7-ethoxy coumarin (ECOD) in long-term cultures of cryopreserved cells (up to 14 days). The albumin secretion rate was 62% that of non-cryopreserved cells at days 11 and 14. The ECOD activity was 54% that of fresh, control cells initially and increased up to 79% by the 14th day. The urea synthesis rate was stable at 60% that of the control. This study showed that cryopreserved cells can recover liver-specific functions. This result has the potential to dramatically expand the clinical application of bioartificial liver supports.

Targeted Oxygen Delivery within Hepatic Hollow Fiber Bioreactors via Supplementation of Hemoglobin-Based Oxygen Carriers

Hepatic hollow fiber bioreactors are considered a promising class of bioartificial liver assist device (BLAD). Unfortunately, limited oxygen (O(2)) transport to hepatocytes within this device hinders further development. Hepatocytes in vivo (in the liver sinusoid) experience a wide range of oxygen tensions (pO(2) = 25-70 mmHg), which is important for development of proper differentiated function (zonation). Previously, we observed that bovine red blood cell (bRBC) supplementation of the circulating media stream enhanced oxygenation of cultured C3A hepatoma cells compared to a culture with no O(2) carrier (Gordon, J.; Palmer, A. F. Artif. Cells, BloodSubstitutes, Biotechnol. 2006, 33 (3), 297-306). Despite this success, the cells were not exposed to the desired in vivo O(2) spectrum (Sullivan, J.; Gordon, J.; Palmer, A. Biotechnol. Bioeng. 2006, 93 (2) 306-317). We hypothesize that altering the kinetics of O(2) binding/release to/from hemoglobin-based O(2) carriers (HBOCs) could potentially target O(2) delivery to cell cultures. High P(50) (low O(2) affinity) HBOCs preferentially targeted O(2) delivery at high inlet pO(2) values. Conversely, low P(50) (high O(2) affinity) HBOCs targeted O(2) delivery at low inlet pO(2) values. Additionally, inlet pO(2), flow rate, and HBOC concentration were varied to find optimal bioreactor operating conditions. Our results demonstrate that HBOCs can enhance O(2) delivery to cultured hepatocytes, while exposing them to in vivo-like O(2) tensions, which is critical to create a fully functional BLAD.

Differentiation of mesenchymal cells derived from human amniotic membranes into hepatocyte-like cells in vitro

Mesenchymal stem cells are believed to be involved in the formation of mesenchymal tissues, including bone, cartilage, muscle, tendon and adipose tissue. Interestingly, it has previously been reported that mesenchymal stem cells could also differentiate into endoderm-derived cells, such as hepatocytes. The amniotic membrane contains mesenchymal cells and is a readily available human tissue. Therefore, we investigated the potential of mesenchymal cells derived from human amniotic membrane (MC-HAM) to differentiate into hepatocytes. We analyzed the expression of hepatocyte-specific genes in MC-HAM before and after induction of differentiation into hepatocytes. We observed the expression of mRNAs encoding albumin, a-fetoprotein, cytokeratin 18 and alpha1-antitrypsin, but not those encoding glucose-6-phosphatase or ornithine transcarbamylase, prior to the induction of differentiation. However, immunocytochemistry revealed that albumin and alpha-fetoprotein were abundantly produced only after the induction of differentiation into hepatocytes. In addition, we observed the storage of glycogen, a characteristic feature of hepatocytes, using periodic acid-Schiff staining of MC-HAM induced to differentiate into hepatocytes. Overall, MC-HAM appear to be able to differentiate into cells possessing some characteristics of hepatocytes. Although further studies should be carried out to determine whether such in vitro-differentiated cells can function in vivo as hepatocytes. These cells may be useful in various applications that require human hepatocytes.

Evaluation of a galactose-carrying gelatin sponge for hepatocytes culture and transplantation

This study proposes a new three-dimensional culture of mouse hepatocytes in a porous galactose-carrying modified gelatin sponge matrix. The modification of gelatin using galactose residues significantly increased the attachment of hepatocytes on the substrate. A modified gelatin sponge with lactobionic acid (MGLA) was prepared to increase the specific interaction between the hepatocytes and the matrix. Hepatocytes cultured in a three-dimensional MGLA sponge released much less lactate dehydrogenase than those cultured on a collagen Type I-coated monolayer. Moreover, the survival rate of hepatocytes cultured on an MGLA sponge was longer than the survival rate of hepatocytes cultured on a collagen Type I-coated monolayer. Hepatic specific metabolic functions, namely, the secretion of serum albumin and the synthesis of urea, were well maintained and promoted by spheroidal hepatocytes formed in the MGLA sponge.

Low asialoglycoprotein receptor expression as markers for highly proliferative potential hepatocytes

Development of a reliable method to isolate highly proliferative potential hepatocytes will provide insight into the molecular mechanisms of liver regeneration, as well as proving crucial for the development of a biohybrid artificial liver. The aim of this study is to isolate highly proliferative, e.g., progenitor-like, hepatocytes. To this end, we fractionated hepatocytes expressing low and high levels of the asialoglycoprotein receptor (ASGP-R) based on the difference in their adhesion to poly[N-p-vinylbenzyl-O-beta-d-galactopyranosyl-(1-->4)-d-gluconamide] (PVLA), and examined the proliferative activity and gene expression of these fractionated hepatocytes. The results showed that approximately 0.5 to 1% of the total number of hepatocytes, which showed low adhesion to PVLA, expressed low levels of the ASGP-R, while the rest of hepatocyte population with high adhesion to PVLA expressed high levels of the ASGP-R. Interestingly hepatocytes with low ASGP-R expression levels had much higher DNA synthesizing activity (i.e., are much more proliferative) than those with high ASGP-R expression levels. Moreover, hepatocytes with low ASGP-R expression levels expressed higher levels of epidermal growth factor receptor (EGF-R), CD29 (beta1 integrin) and CD49f (alpha6 integrin) and lower levels of glutamine synthetase than those with high ASGP-R expression. These findings suggested that hepatocytes with low adhesion to PVLA due to their low ASGP-R expression could be potential candidates for progenitor-like hepatocytes due to their high proliferative capacity; hence, the low expression of the ASGP-R could be a unique marker for progenitor hepatocytes. The isolation of hepatocytes with different functional phenotypes using PVLA may provide a new research tool for a better understanding of the biology of hepatocytes and the mechanisms regulating their proliferation and differentiation in health and disease.

Oxygen transfer in a convection-enhanced hollow fiber bioartificial liver

A mathematical model was developed to predict oxygen transport in a hollow fiber bioartificial liver device. The model parameters were taken from the HepatAssist 2000 device, a plasma perfused hollow fiber cartridge with primary hepatocytes seeded in the extracapillary space. Cellular oxygen uptake was based on Michaelis-Menten kinetics. Oxygen transport due to the convective flow of plasma into the extracapillary space was considered. The effect of modulating several important parameters was investigated, namely, the Michaelis-Menten constant V(m) (the maximum oxygen consumption per unit volume of the cell mass), the oxygen partial pressure, the flow rate of the plasma at device inlet, and the permeability of the cell mass contained in the extracapillary space. A computer implementation of the model was used to assess whether a given number of cells could be maintained within such a device. The results suggest that a substantial proportion of the hepatocytes are exposed to hypoxic conditions under which metabolism may be impaired.

Improvement of metabolic performance of cultured hepatocytes by high oxygen tension in the atmosphere

Maintaining metabolic functions of cultured hepatocytes at higher levels is an essential requirement for the development of a bioartificial liver. We investigated the effect of oxygen tension (10--40%) of the medium on immobilization efficiency and metabolic functions of cultured hepatocytes obtained from a rat for up to 4 days. Immobilization efficiencies of cultures in 10% oxygen showed a significantly lower value from those for the other conditions. The ammonium metabolic rate and the albumin secretion rate were significantly improved with an increase of dissolved oxygen tension for up to 2 days. These values remained similar in the later stage of the culture. The urea secretion rate showed similar values in all conditions. In conclusion, higher oxygen tension improved immobilization efficiency and metabolic functions of cultured rat hepatocytes in the earlier stage of culture for up to 2 days.

Design of a fluidized bed bioartificial liver

The aim of this study was to design a bioreactor for extracorporeal liver supply containing alginate beads in a fluidized bed regimen. The objective was to achieve a satisfactory mixing into the bioreactor to promote the potential exchanges and mass transfers. First, we checked whether both present phases (solid: alginate beads; liquid: saline solution at 20 degrees C) might allow for this fluidization. Then the optimal design was defined as a function of the required operating conditions, bead volume, and perfusion flow rate; the bioreactor cross section and height especially needed to be adjusted. The efficient fluidization, under optimized conditions, was proven through the follow-up of the head losses generated by the fluidized bed. Criteria for scaling up were also determined.

Is there a future for liver-assist devices?

Patients with fulminant hepatic failure fall into two categories: those who will not recover without hepatic replacement, and those with severe but potentially reversible liver injury whose livers have the potential to recover and/or regenerate. Liver support systems must provide physiologic support, rendering the patient hemodynamically stable and "bridging" the patient to transplantation, or allowing the native liver to recover and/or regenerate. Recent limited successes with bioartificial liver support for patients with fulminant liver failure are encouraging. However, these preliminary results come without randomization or control groups and without stratification by disease etiology or severity. It is hoped that randomized, controlled trials will answer important questions about the efficacy of these systems.

A new concept of bioartificial liver based on a fluidized bed bioreactor

Many bioartificial livers have been developed, but most of them suffer from difficulty when being scaled up and from poor efficiency of mass transfer between the plasma and the immobilized hepatocytes. We present a new concept of bioartificial liver based on the fluidized bed motion of hepatocytes entrapped in alginate beads. The bioreactor is designed to offer stable behavior. The maximum fluid perfusion velocity is determined to avoid any bead release from the bioreactor. The fluidized bed height depends on the amount of beads and the velocity employed. Under the optimized operating conditions, the mass transfer between perfusion fluid and beads is very efficient; only 10 min are necessary to reach concentration equilibrium. Hence, this fluidized bed bioartificial liver appears to be a promising tool for a liver support system in the treatment of acute liver failure.

Review article: the management of acute liver failure

Acute liver failure (ALF) is a relatively uncommon but dramatic clinical syndrome with high mortality rates, in which a previously normal liver fails within days or weeks. Paracetamol overdose remains the major cause of ALF in the UK, while viral hepatitis is the commonest cause world-wide. Cerebral oedema is the leading cause of death in patients with ALF. Despite advances in intensive care and the development of new treatment modalities, ALF remains a condition of high mortality best managed in specialist centres. Orthotopic liver transplantation is the only new treatment modality that has made a significant impact in improving outcome. Bioartificial liver support systems and hepatocyte transplantation are new promising treatment options that may change the management of ALF in the future.